Underground lawn sprinkers are well known and typically comprise a hollow housing buried in the ground having a fluid inlet connected to a water supply line. The housing also includes a fluid outlet through which the water admitted to the housing is expelled. Various types of nozzles may be screwed onto or otherwise associated with the outlet for distributing this expelled water in any suitable pattern over a ground surface. Check valves have often been used with each of the sprinkler heads in an irrigation system to resist the static head pressures normally seen by the heads to prevent low head drainage. Some improved check valves are disclosed in U.S. Ser. Nos. 482,797 and 489,432, both now abandoned, assigned to The Toro Company, the assignee of the present application.
In northern climates where freezing temperatures are a problem during the winter, it is necessary to drain the irrigation system at the conclusion of the irrigation season to prevent damage to the system. This is often done by opening a drain valve at the low point in the system of water supply lines leading to the sprinkler heads. Sometimes, the draining operation is done by blowing compressed air through the water supply lines to blow out the water in the irrigation system through the sprinkler heads themselves.
When check valves are used with the sprinkler heads, the problem of draining water from the heads is complicated because the check valves open only one way and do not allow water to drain downwardly out of the valves and into the water supply lines. Thus, the method of draining which comprises simply opening a drain cock in the water supply lines is ineffective for removing any water in the head which is trapped or retained above the check valve. Moreover, even when the draining method comprises blowing compressed air through the lines, the sprinkler heads often have various cavities which serve to trap pockets of water which are retained in the head by the check valve even after the air is shut off. If this water is allowed to remain in the head over the winter, freezing will, of course, cause the water to expand and often cause damage to the sprinkler head, e.g. by forcing or blowing the top of the head off or otherwise doing damage to other of the internal parts of the head.
Applicants are aware of one type of prior art sprinkler head having means for draining water out of the housing downwardly through the fluid inlet. These heads, known as valve-in-head models (such as the Toro models 690-01 and 690-03), utilize a main valve comprising a cylindrical valve member that seals against the fluid inlet. This main valve has to be opened to allow water at the inlet to pass through the nozzles and otherwise cause the sprinkler head to operate. While this main valve is not a check valve per se, when closed it normally retains water in the sprinkler head. Thus, there is a need for draining water out of the housing of such a head.
In these prior art valve-in-head models, the water draining operation was accomplished by placing into the main valve a drain passageway extending through the main valve between the fluid inlet and the interior of the sprinkler head housing. This passageway terminated at its lower end in a drain port on the lower face of the main valve directly adjacent the fluid inlet. A cylindrical chamber defined by a screen was formed around the drain port on the lower face of the main valve. This chamber comprised a means for holding a ball and O-ring in close proximity to the drain port. Normally, water pressure at the inlet would keep the ball biased upwardly against the O-ring to close the drain port and prevent water from draining out of the sprinkler head housing. However, when water was exhausted out of the fluid inlet by opening a drain cock or the like in the water supply lines, the ball could fall by gravity away from the port and then allow any water remaining in the housing to drain down into the fluid inlet.
While the drain valve noted above is effective in accomplishing the desired result, it has a number of disadvantages. First, it utilizes a number of parts adding to the cost and complexity of the head, the parts namely being the O-ring, the ball, the chamber or some similar structure required for holding the ball and O-ring adjacent the drain port, and finally the drain port and the relatively extended passageway for connecting the fluid inlet and the interior of the housing through the main valve. Moreover, it is relatively difficult and time-consuming to assemble or construct such a drain valve into the main valve structure, especially because of the smallness of the ball and other parts. This further increases product cost.